Elizabeth, NJ, United States
Elizabeth, NJ, United States

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Grenko J.A.,North Carolina State University | Reynolds Jr. C.L.,North Carolina State University | Barlage D.W.,North Carolina State University | Johnson M.A.L.,North Carolina State University | And 5 more authors.
Journal of Electronic Materials | Year: 2010

We report on the growth of Al 0.25Ga 0.75N/GaN heterostructures grown on low dislocation density vicinal surfaces of semi-insulating c-axis GaN substrates. Atomic force microscopy (AFM), photoluminescence (PL), cathodoluminescence (CL), high-resolution x-ray diffraction (HRXRD), secondary-ion mass spectroscopy (SIMS), Hall effect, and Raman spectroscopy have been used to assess structural and electrical properties as a function of substrate offcut. Bulk GaN substrates with vicinal offcut between 0.5° and 1.4° are optimal with respect to surface roughness and dopant incorporation. AFM, PL, and CL show decreasing Mg incorporation with increasing offcut angle. Raman spectroscopy, used to analyze biaxial strain, confirms essentially strain-free heterostructure growth on vicinal substrates with offcut angles between 0.5° and 1.4° off [0001] toward [1100]. Aluminum (Al) incorporation in the Al xGa 1-xN barrier assessed by Raman vibration is in excellent agreement with trends found by HRXRD. © 2010 TMS.

Grenko J.A.,North Carolina State University | Ebert C.W.,Veeco Turbodisc | Reynolds Jr. C.L.,North Carolina State University | Duscher G.J.,University of Tennessee at Knoxville | And 5 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2010

Wereport on the growth of Al 0.25Ga 0.75N/GaN heterostructures on low dislocation density semi-insulating c-axis GaN substrates by metalorganic vapor phase epitaxy (MOVPE). A room temperature (RT) Hall mobility (μRT) up to 2065 cm2V -1 s -1 at sheet density (n s) of 8.25×1012 cm -2 has been measured. This work compliments prior studies in which we observed a buffer-induced modulation of the RT twodimensional electron gas (2DEG) n s and μ RT by varying the GaN buffer layer thickness. Here, we focus on the optimization of the heterostructure 2DEGproperties by elimination of silicon doping in the Al 0.25Ga 0.75N barrier and unintentional Al in the not-intentionally doped (n.i.d.) GaN buffer layer. The 15% improvement in μRT and n s relative to previous results is consistent with those predicted by Poisson solver calculations. Use of thick GaN buffers has minimized the theoretical mobility reduction based on intersubband scattering and has enabled us to determine the 2DEG sheet density associated with the polarization field (n polar s) to be ∼5×10 12 cm -2. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhang X.G.,Veeco Turbodisc | Soderman B.,Veeco Turbodisc | Armour E.,Veeco Turbodisc | Paranjpe A.,Veeco Turbodisc
Journal of Crystal Growth | Year: 2011

Increasing demand for high brightness LEDs for LCD TV backlighting and solid-state lighting requires MOCVD growth of GaN at high growth rates (>5 μm/h) with high crystalline quality in mass production reactors. Understanding the MOCVD growth parameters on the quality of GaN materials and growth efficiency are important for quickly setting up process windows for the optimization and qualification of new LED growth processes. We have investigated the effects of N 2/H 2 ratio, N 2/NH 3 ratio, and growth temperature on the growth efficiency, crystal quality, morphology, yellow-band emission (YE), and sheet resistance of un-doped GaN epitaxial layers using design of experiment (DOE) methodology. Our results indicate that high growth temperature (at 1080 °C) and low N 2/H 2 ratio (set at 0.5 in the DOE) were the common factors for achieving better crystal quality, smoother surface, and lower YE intensity in GaN epitaxial layers, as well as for obtaining higher growth efficiency in MOCVD of GaN. © 2010 Elsevier B.V. All rights reserved.

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